This invention relates generally to the field of additive manufacturing. In particular, the invention relates to an additive manufacturing process enabling the measurement of residual stresses at specific locations in components.
Additive manufacturing is a process by which parts can be made in a layer-by-layer fashion by machines that create each layer according to an exact three dimensional (3D) computer model of the part. In powder bed additive manufacturing, a layer of powder is spread on a platform and selective areas are joined by sintering or melting by a directed energy beam. The platform is indexed down, another layer of powder is applied, and selected areas are again joined. The process is repeated for up to thousands of times until a finished 3D part is produced. In direct deposit additive manufacturing technology, small amounts of molten or semi-solid material are applied to a platform according to a 3D model of a part by extrusion, injection or wire feed and energized by an energy beam to bond the material to form a part. Common additive manufacturing processes include selective laser sintering, direct laser melting direct metal deposition, and electron beam melting.
Once the component is manufactured, the component is incorporated into a system to be used for a specific function. An example is a gas turbine engine. During operation, the component is exposed to thermal and mechanical environments that stress the component. The stresses and resulting strain experienced by the component cause residual stresses and possible structural failures or cracks in the component.
Several non-destructive techniques exist to detect crack growth or residual stresses in components. Current non-destructive techniques expose the component to external probes such as electromagnetic fields, dyes, or ultrasonic waves. It is difficult to obtain localized information at pre-determined locations in a component with the current technologies, for example at regions of increased service stresses. Current technologies mostly detect flaws after they have formed, and are far less sensitive to the stage leading up to the formation of flaws, for example, internal cracks.